A pregnant porbeagle shark has potentially become prey to a great white shark near Bermuda, marking the first documented instance of such predation.
In October 2020, researchers tagged a pregnant porbeagle shark (Lamna nasus) off Cape Cod, Massachusetts, as part of a study on the migratory patterns of pregnant sharks.
The study utilized pop-off tags that monitor the depth and temperature of the shark. Once the tag detaches and surfaces, it transmits the collected data back to researchers.
Five months post-tagging, data revealed movements of the shark southwest of Bermuda, where it traveled at depths of 600 to 800 meters during the day and 100 to 200 meters at night, with temperature fluctuations from 6.4 to 23.5°C (43.5 to 74.3°F).
However, starting March 24, 2021, the recorded temperature around the shark shifted to a range of 16.4°C to 24.7°C (61.5°F to 76.5°F) while it maintained similar depths. This alteration in temperature and diving behavior suggests the shark and its tag were most likely consumed, according to researchers.
“All our evidence points to the same conclusion,” stated a lead researcher. “It’s clear that our porbeagle shark was eaten by another shark.” The great white shark (Carcharodon carcharias) is considered the most likely predator, given its size and predatory behavior in the area.
“This was a big female shark that got eaten,” commented a team member, emphasizing that the predator would need to be larger than the porbeagle to execute such an attack.
The predation event likely occurred opportunistically at a depth of about 300 meters in the open ocean, where prey is sporadically available. “A large pregnant porbeagle shark would provide a significant meal,” researchers noted.
Porbeagle sharks, which are classified as endangered, inhabit the Atlantic Ocean, South Pacific Ocean, and Mediterranean Sea. They can reach lengths of up to 3.7 meters, weigh as much as 230 kilograms, and live for around 65 years. Female porbeagles typically begin reproducing at 13 years of age, birthing around four pups every one to two years with a gestation period of 8 to 9 months.
While shark-on-shark predation is not uncommon, targeting a large shark in deep water is unusual. This incident marks the first confirmed case of a porbeagle being consumed by another shark.
If such predation events are occurring more frequently, it poses a worrying trend for conservation efforts. “In one instance, the population has lost a significant reproductive female and her potential offspring,” a researcher noted. “This emphasizes the importance of ongoing studies into the predation dynamics affecting porbeagle sharks.”
However, some experts caution that the findings do not definitively confirm a shark was responsible for the predation. Other predators, such as orcas, have also been known to prey on large sharks. “While there was an obvious predation event, it is not certain that it involved only lamnid sharks,” an expert commented.
Subsequently, another tagged shark from the same research team also perished at a similar depth near Bermuda a year later, though that shark sank to the ocean floor. Researchers believe this may indicate a separate predation incident where the shark was only partially consumed.
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